The present invention relates generally to fasteners and more specifically to two piece fasteners which are adapted to be utilized in securing a broad range of material thicknesses.
In some applications it would be desirable to use a two piece fastener of the type employing a pin having combination locking and breakneck grooves and a tubular member adapted to be swaged thereto and in which any of these grooves is capable of functioning as a breakneck so as to enable a single fastener to be utilized over a broad range of material thicknesses. One problem with such a fastener is providing a structure in which the pin break will occur repeatedly and consistently in a desired one of the combination grooves.
This is accomplished by the present invention which utilizes a pin having a unique combination groove geometry. In addition, it is believed that the use of a selective relative hardness between the pin and associated tubular member further assists in the proper functioning of the fasteners. In the present invention, an axially directed force generated by the swaging of the tubular member into a preselected one of the combination grooves is utilized at a preselected groove which force when combined with a pulling force applied via a plurality of jaws by an installation tool will provide a combined tensile force at the selected groove whereby fracture will occur and hence that groove when selected functions as a breakneck. The groove geometry includes a pair of radially outwardly diverging sidewalls defining each groove, each of which sidewall forms a different angle with respect to a radial plane extending transversely through the pin member and controlled radius portions interconnecting adjacent end portions thereof.
Because of the unique contour of the combination grooves, conventional jaw structures in the installation tool may in some cases have reduced life and hence a modified jaw structure having teeth with a contour more closely matching that of the combination grooves may be desirable; however, in some cases it would be advantageous to be able to utilize tools with existing jaw structures. Thus in one form of the invention the end portion of the pin is provided with a plurality of pull grooves which are contoured differently from the combination grooves and which are adapted for use with existing jaw structures.
Accordingly, the present invention provides an improved two piece fastener having combination locking and breakneck grooves which extend along the shank portion of the pin a distance at least equal to the length of the shank portion less the minimum material thickness for which such fastener is to be used. This invention thereby enables a single fastener to be utilized to secured materials having a wide variety of total thicknesses. This feature affords substantial cost savings to users of such fasteners both by reducing the number of different fasteners required to be purchased and carried in their inventory as well as increasing product reliability by reducing the likelihood of a fastener with an inappropriate gripping range being inadvertently used. In one form of the invention an end portion of the pin is provided with a plurality of pull grooves of a shape different from that of the combinatin grooves with the pull grooves being adapted for use with existing jaw structures.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.